AProject Report

OnTHERMOELECTRIC POWERED CAR

SUBMITTED IN PARTIAL FULFILLMENT OF THE DEGREEOF

BACHELOR OF TECHNOLOGYIN

MECHANICAL ENGINEERING

DEPARTMENT

Submitted By

MUNISH KUMAR(7986)

NIKHIL GHARIA(7988)

SURESH KUMAR(8021)

ATUL(6953)

AKSHAY(6954)

Mechanical Engineering DepartmentLR Group of Institute of Engineering And Technology

SESSION 2012-2016

ABSTACT

The main aim of Major project is to expose the student to the industrial technical problems to

which he is to be exposed in the future life. In an organization where Making Things Right in the

first instance is the driving motto, perfection and accuracy are inevitable.

I have worked for three months on the topic entitled “THERMOELECTRIC POWERED CAR ”. I have the honor to work as a student of LR Group to the extent of my technical

capabilities. Doing this tenure, I have acquired a sufficient knowledge on turbines

I remained actively associated with one of the most demanding field of Energy. The time spent

on the aforesaid topic has really proved to be very useful and will remain enduring throughout

my professional career. Brief outline of the work is covered under the following heads.

SEEBACK EFFECT PELTIER EFFECT & PELTIER PLATES HEAT TRANSFER AND BASIC HEAT SINK DESING AND SURFACE AREA CALCULATION RESULT MODIFICATIONS SUGGESTION FOR FUTURE MODIFICATION AND FUTURE SCOPE OF

PROJECT

In conclusion, I must say that the Major project has helped me to enhance my working skills &

stamina and to further enlighten me to enter a new phase of life after completion of the degree

program.

TABLE OF CONTENTS

Chapter No. Name

1 INTRODUCTION AND BASIC

1.1 Aim of project

1.2 Concept

1.3 Need of project

1.4 Efficiency

1.5 Proposed Design

1.6 Facility Required

1.7 Application

2 PELTIER PLATE

2.1 what is peltier plate

2.2 What is material of peltier plate

2.3 Marking of peltier plate

2.4 Peltier plate characteristic and Operation curve

2.5 uses of peltier plate

3 HEAT SINK

3.1 Introduction

3.2 Working Principle of heat sink

3.3 Design parameter of heat sink

3.4 Engineering application of heat sink

3.5 Performance of heat sink

4 RESULT

4.1 Result modification and future scope

4.2 Efficiency of peltier plate

4.3 Refrence

CHAPTER-1

INTRODUCTION & BASIC

1. AIM OF THE PROJECT

This concept behind the project is thermoelectric generation that has been known from

sometime, but the practical implementation of this concept is quite difficult. The idea behind this

project is to make a Car that is powered by thermoelectric source, i.e. to build a car that moves

with temperature difference. This concept has not been explored earlier but a lot of research can

be done in this regard. We will be presenting a practically running model of a car driven by a

simple heat source with the help of thermoelectric generator.

2. CONCEPT

The world wastes a lot of heat. Between half and two-thirds of the fuel we burn to create energy

is dissipated as heat into the atmosphere. While it has been long known that waste heat can be

converted into energy, the low efficiency of early thermoelectric generation systems was such

that it limited the process’s usefulness. TEGs can take waste heat from energy generation or

industrial processes and convert it into electricity. TEGs can provide electricity to a load directly

when a constant heat source is available, or they can be used in combination with batteries if the

heat source is not constant. A typical TEG is made of bismuth-telluride semiconductors

sandwiched between two metallized ceramic plates.

Because TEGs eliminate the need for wires and batteries, their primary applications have been in

remote places where the use (and replacement) of batteries is impractical or impossible, such as

in offshore engineering operations, lighthouses, oil pipelines and remote telemetry and data

collection in satellites and spacecraft. (NASA’s Curiosity rover uses radioisotope thermoelectric

generators that produce power by converting the heat generated by the decay of plutonium-238

fuel into electricity.) They have a number of small but increasingly important applications in

manufacturing, data centers, the automotive industry and in military applications.

Our Idea is to convert this concept into a vehicle or a car that is powered directly from heat

without any fuel. That is to make a thermoelectric powered car. It is different from the solar

powered car that runs with the help of light and works only in day time, in a way that

Thermoelectric powered car is a powerful and efficient method to drive the car with the help of

temperature difference, that one side of the peltier plate involved is heated and other side is

cooled by placing appropriate heat sink over it that is cooled with the help of normal atmospheric

air while the car will be moving.

3. PRINCLIPLE OF OPERATION BEHIND THERMOELECTRIC POWERED CAR

This concept is very useful in terms that it adds up to other renewable sources of energy and can

be used in place of other non-conventional sources of energy like wind, solar, tides, geothermal

heat, etc. This is a new concept for electricity generation using temperature difference between

junctions of a peltier element to be used in our project. The complete Thermo Electric Generator

would be based on Seebeck Effect that is reverse of peltier effect. The thermoelectric effect is the

direct conversion of temperature differences to electric voltage and vice-versa. A thermoelectric

device creates a voltage when there is a different temperature on each side. Conversely, when a

voltage is applied to it, it creates a temperature difference. At the atomic scale, an applied

temperature gradient causes charge carriers in the material to diffuse from the hot side to the cold

side, similar to a classical gas that expands when heated; hence inducing a thermal current. A

Peltier cooler can also be used as a thermoelectric generator. When operated as a generator, one

side of the device is heated to a temperature greater then the other side, and as a result, a

difference in voltage will build up between the two sides (the Seebeck effect).

3. NEED AND SIGNIFICANCE OF THERMOELECTRIC POWERED CAR

Less than 30% of the energy in a gallon of gasoline reaches the wheels of a typical car; most of

the remaining energy is lost as heat. Since most of the energy consumed by an internal

combustion engine is wasted, capturing much of that wasted energy can provide a large increase

in energy efficiency. For example, a typical engine producing 100 kilowatts of driveshaft power

expels 68 kilowatts of heat energy through the radiator and 136 kilowatts through the exhaust.

The possibilities of where and how to utilize this lost energy are explored with this project. The

solution of recovering heat energy from the car engine through a thermoelectric generator using

peltier plates has been proposed. This electricity generated through the thermoelectric generator

from waste heat of the engine could be used to charge the car batteries or operate any electrical

device within or outside the car. Also, in other application of this thermoelectric generator that is,

Electricity generation from glaciers / ice is another alternative for electricity generation through

other non –renewable resources of electricity and yet to be explored. The idea behind this project

is to utilize a small temperature difference between the ice / cold water and some atmospheric

heat to produce electricity and drive a car using this electricity by designing an efficient

thermoelectric powered car.

4. EFFICIENCY CALCULATION

The efficiency of an ATEG is governed by the thermoelectric conversion efficiency of the

materials and the thermal efficiency of the two heat exchangers. The ATEG efficiency can be

expressed as:

ζOV = ζCONV х ζHX х ρ

Where:

ζOV : The overall efficiency of the ATEG

ζCONV : Conversion efficiency of thermoelectric materials

ζHX: Efficiency of the heat exchangers

ρ : The ratio between the heat passed through thermoelectric materials to that passed from the hot

side to the cold side

4. PROPOSED WORKING OF THERMOLECTRIC POWERED CAR

The design would include the use of Peltier plates as the base material for thermoelectric

conversion. This system utilizes the low temperature difference between two hot and cold

junctions of peltier element to generate pollution free electricity without any moving or bulky

parts using the latest technology of thermoelectric generation using peltier plates. This system

should be economical, easy to implement and does not produce any pollution as other generators

available in the market. The amount of electrical power generated is given by I2RL, or VI.

Thermoelectric Generator (TEG’s) are constructed using two dissimilar semi-conductors, one n-

type and the other p-type (they must be different because they need to have different electron

densities in order for the effect to work). The two semiconductors are positioned thermally in

parallel and joined at one end by a conducting cooling plate (typically of copper or aluminum). A

voltage is applied to the free ends of two different conducting materials, resulting in a flow of

electricity through the two semiconductors in series. And when the temperature difference is

maintained by heating element in one side and cooling element in other side, thermoelectric

current flows through the junction and voltage is obtained at the output of TEG. As a result of

the temperature difference, Peltier cooling causes heat to be absorbed from the vicinity of the

cooling plate, and to move to the other (heat sink) end of the device.

Peltier Plate inner view and actual picture is shown below:

Figure 1: a) Peltier Plate actual View b) Peltier Plate TEG inner view

The heat is carried through the cooler by electron transport and released on the opposite ("hot")

side as the electrons move from a high to low energy state. When the two materials are

connected to each other by an electrical conductor, a new equilibrium of free electrons is

established. Potential migration creates an electrical field across each of the connections. When

current is subsequently forced through the unit, the attempt to maintain the new equilibrium

causes the electrons at one connection to absorb energy, while those at the other connection

release energy. In practice many TEG pairs (or couples), such as described above, are connected

side-by-side, and sandwiched between two ceramic plates, in a single TEG unit.

Figure 2: Proposed Working of a Thermoelectric Generator

The heat pumping capacity of a cooler is proportional to the current and the number of pairs in

the unit.

5. PROPOSED DESIGN OF THERMOELECTRIC POWERED CAR

Thermoelectric Powered Car should include a heat source that provides the high temperature,

and the heat flows through a thermoelectric converter to a heat sink, which is maintained at a

temperature below that of the source. This would be done with the help of a Heat Sink. The

temperature differential across the converter produces direct current (DC) to a load (RL) having a

terminal voltage (V) and a terminal current (I). This voltage is then provided to the car that has

Chassis as shown in the proposed design , a heat exchanger , heat sink , mechanical couplings

and peltier plates. There is no intermediate energy conversion process. For this reason,

thermoelectric power generation is classified as direct power conversion.

Heat Sink Heat Exchanger

Copper Sheet Pillar Rods

Peltier Plate Aluminum Sheet

Heat source

Chassis

Figure 2: Proposed Design of thermoelectric car

6. FACILITIES REQUIRED

1. Peltier Plates (TEC-12706), operating voltage: 12V, size: 4 x 4 cm, thickness : 5mm

2. Heat Sink: To be designed to increase the surface area of cold junction of peltier plate to

increase the electricity and efficiency of the thermoelectric generator .Material: Aluminium

3. Heat sink compound and Thermal paste (Adhesives) to mount peltier element on heat sink.

4. Base container 9Aluminium) for setup of the generator

5. Clamps to mount heat sink on base plates

6. Support shafts to provide height to heat sink (Aluminium)

7. Other tools and equipments: Nut-bolt pairs, screwdrivers, multimeters, Drillling machine,

lathe machine, surface grinding machine

8. Output devices, load to show the generated electricity.

9. Chassis of Car

10. Wheels and hubs

11. Clamps for mounting wheels

12. Motors (12V,30 rpm)

APPLICATIONS

Self-powering machine sensors. Manufacturing facilities and data centers run large amounts of

equipment that must be kept cool to operate at maximum efficiency. Sensors can help make sure

equipment doesn’t overheat, but sensors that, themselves, must be plugged in add to the heat

loads. TEG-powered sensors located at machine hot spots can power themselves using ambient

heat while monitoring and communicating problems to operations personnel.

The sensors can provide information such as temperature, humidity, wear and tear, and whether

parts need maintenance or replacement. If these intelligent network sensors are activated only

when sending or receiving data, the amount of energy they require is tiny (on the milliwatt

scale), and only the smallest thermoelectric generators/sensors are required.

Printed thermogenerators. While printed electronics, an application of nanotechnology, have

the potential to revolutionize the electronics industry, thermogeneration may also a beneficiary.

Researchers at Germany’s Fraunhofer Institute for Manufacturing Technology and Advanced

Materials (IFAM) will soon introduce a printed thermogenerator that can be tailored exactly to

technical interfaces.

In the case of self-powered machine sensors, components often need to be highly customized to

particular machines and operations. The new printed thermogenerators ultimately mean that

manufacturers, data centers and others that operate complex machinery might literally customize

and print, on their own, the sensors they require — sensors that are less susceptible to faults

because the energy supply can be adapted directly to the equipment.

“Generative manufacturing processes produce both sensors and sensor networks, as well as the

required elements for energy harvesting, such as thermo generators, by directly depositing

functional structures, which have an ink or paste base, using ink-jet, aerosol-jet, screen-printing

or dispensing processes,” says Dr. Volker Zöllmer, head of functional structures at IFAM. “Not

only can electrical circuit boards and sensor elements be attached to different interfaces but it is

also possible to produce structures which harvest energy.”

Automotive. Heat from the exhaust of internal combustion engines can be harvested into energy

with the addition of a thermoelectric generator in the vehicle. With car exhaust reaching

temperatures of about 1,300 deg F, the enormous delta temperature could be capable of

generating between 500 and 750 watts of electricity, which could, for example, charge a battery

in a hybrid vehicle or reduce the load on a car’s alternator, improving fuel economy.

Military. Given how enthusiastic the U.S. military is as of late to develop and further advance

alternative energy sources, thermo generation has attracted the attention of military researchers.

The U.S. Army Research Laboratory (ARL) is currently looking for ways to harness, package

and shrink TEG technology in hopes that it could lead to wearable power sources on soldiers —

using the temperature difference between body heat and outside air — or to more efficient

military vehicles.

Chapter 2

PELTIER PLATES

1.1 what is peltier plate ?

Figure: Peltier Element

The discovery began in the middle of 1821, where J. T. Seebeck discovered that two not similar

metals, if they are connected in 2 different points and those points are held in different

temperatures, there will be a micro-voltage developed. This effect is called the "Seebeck effect"

as of it's discoverer. Some years later, a scientist discovered the opposite of the Seebeck effect.

He discovered that if someone applies voltage to a thermo-couple, one junction shall be heated

and the other shall be cooled. The scientist was called Peltier and the effect called the "Peltier

effect".

A Peltier thermo-element is a device that utilizes the peltier effect to implement a heat pump. A

Peltier has two plates, the cold and the hot plate. Between those plates there are several thermo

couples. All those thermo couples are connected together and two wires come out. If voltage is

applied to those wires, the cold plate will be cold and the hot plate. The device is called a heat

pump because it does not generate heat nor cold, it just transfers heat from one plate to another,

and thus the other plate is cooled. It is also called a thermo-electric cooler or TEC for short.

Because TECs have several thermocouples, a lot of heat is transferred between the plates.

Sometimes it can reach a temperature difference of 80 degrees Celsius or more.

A Peltier thermo-element compared to a AA batteryPeltier coolers, also known as thermoelectric coolers (TEC) consist of the peltier element itself

and a powerful heat sink/fan combination to cool the TEC. TEC coolers have two wires which

connect to a power source in your pc case, when voltage is applied to those wires, a temperature

difference across the two sides of the TEC is achieved. One side is hot and the other side is cool.

You place the TEC between the CPU/GPU and the heat sink with an appropriate thermal

interface material (thermal grease).

Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two

different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state

active heat pump which transfers heat from one side of the device to the other, with consumption

of electrical energy, depending on the direction of the current. Such an instrument is also called a

Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC). They

can be used either for heating or for cooling (refrigeration), although in practice the main

application is cooling. It can also be used as a temperature controller that either heats or cools.[1]

This technology is far less commonly applied to refrigeration than vapor-compression

refrigeration is. The main advantages of a Peltier cooler (compared to a vapor-compression

refrigerator) are its lack of moving parts or circulating liquid, and its small size and flexible

shape (form factor). Its main disadvantage is high cost and poor power efficiency. Many

researchers and companies are trying to develop Peltier coolers that are both cheap and efficient.

A Peltier cooler can also be used as a thermoelectric generator. When operated as a cooler, a

voltage is applied across the device, and as a result, a difference in temperature will build up

between the two sides. When operated as a generator, one side of the device is heated to a

temperature greater than the other side, and as a result, a difference in voltage will build up

between the two sides (the Seebeck effect). However, a well-designed Peltier cooler will be a

mediocre thermoelectric generator and vice-versa, due to different design and packaging

requirements.

2.2 What are Peltier elements made of?

Peltier thermo-elements are mainly made of semi conductive material. This means that they have

P-N contacts within. Actually, they have a lot of P-N contacts connected in series. They are also

heavily doped, meaning that they have special additives that will increase the excess or lack of

electrons.

The following drawing shows how the P-N contacts are connected internally within a Peltier

TEC:

 

Now, imagine tens or hundreds of those P-N material between two plates. The following drawing

shows how many P-N contacts can exist in a rectangular area like a Peltier TEC.

 

You can see how the P and N material are connected in series together to implement a long strip

of P-N junctions. The top plate is the hot plate and the bottom is the cold plate. When power is

applied to the two wires, the heat will be transfered from the cold plate to the hot plate and thus

THE COLD PLATE SHALL COLD.

2.3 PELTIER MARKINGS

Sometimes, the TECs have identification markings on their face, just like the following

picture:

 

In this picture you see the ID: TEC1-12709

The first two digits shall be always "TE"

The next digit shall be "C" or "S". "C" stands for standard size and "S" for small sized.

The following digit is a number and indicates the number of stages that the TEC has. In

our example (and the vast majority of TECs) is a one-stage TEC

Right next comes a dash. After the dash, the 3 first digits indicates the number of couples

that the TEC has inside. In our case it has 127 couples. If the couples are 2-digit, then the

number has a leading zero, for example 062 for 62 couples.

Next comes two more numbers that indicate the rating current of operation for the Peltier.

In our case this is 9 Amperes

Sometimes follows a "T" and three numbers. This indicates the maximum operating temperature for the TEC. For example, "T125" is 125°C rated.

PERFORMANCE OF PELTIER ELEMENTS

Thermoelectric junctions are generally only around 5–10% as efficient as the

ideal refrigerator (Carnot cycle), compared with 40–60% achieved by conventional compression

cycle systems (reverse Rankine systems using compression/expansion). Due to the relatively low

efficiency, thermoelectric cooling is generally only used in environments where the solid state

nature (no moving parts, maintenance-free, compact size) outweighs pure efficiency.

Peltier (thermoelectric) cooler performance is a function of ambient temperature, hot and cold

side heat exchanger (heat sink) performance, thermal load, Peltier module (thermopile)

geometry, and Peltier electrical parameters.

Figure: Peltier element schematic. Thermoelectric legs are thermally in parallel and electrically

in series

2.4 PELTIER CHARACTERISTICS AND OPERATION CURVE

Peltier elements can give more than to 80°C temperature difference between their plates. But this

is not a standard value. Actually, this would only be achieved in ideal conditions. The actual

temperature difference (ΔT) is usually smaller. The specifications of a TEC usually show the

achieved temperature difference in conjunction to the power transferred in watts. The diagram

should look like the following:

Looking the above diagram, we can calculate the temperature difference that will be achieved

according to the power that the TEC will have to move across the plates. The power is measured

in watts, but we actually talk about the thermal power. You can use our temperature unit

converter to convert watts to your desired units.

You should not confuse the power of Peltier operation with the power that it transfers. It is most

common that TECs are sold with the electric power indicated. A 125 Watt peltier may NOT be

able to transfer 125 Watts of thermal power across the plates. Instead, it is most possible that it

will draw 125 Watts electric power at max conditions. Peltier comes usually with the datasheet

that indicates the performance curves of the device. Those curves are essential if you want to

make your theoretical calculations for the optimal device operation. The first characteristic curve

for a peltier is the Temperature difference vs Heat pump capacity. This curve indicates the

temperature difference to be achieved in order to pump specific power of heat. It may be one or

more curves for different current loads. An example of such a curve is shown in the following

diagram:

The above curves come from a real Peltier and are not imaginary. What we could conclude from

the above is that if we need for example to transfer 30 Watts of heat, then - with appropriate

voltage as we will see right next - there would be created a temperature difference of 20 degrees

and the TEC would draw as much as 3.02 Amperes. The next characteristic curve is the

Temperature difference VS voltage. With this curve, we can calculate the voltage needed to be

applied on the TEC in order to achieve the appropriate temperature difference. Here is one -also

real- characteristic curve:

2.5 USES:

1. Consumer products

Peltier elements are used in consumer products. For example, Peltier elements are used

in camping, portable coolers, cooling electronic components and small instruments. The cooling

effect of Peltier heat pumps can also be used to extract water from the air in dehumidifiers. A

camping/car type electric cooler can typically reduce the temperature by up to 20°C below the

ambient temperature. With feedback circuitry, peltiers can be used to implement highly stable

temperature controllers that keep desired temperature within +/-0.01 Celsius. Such stability may

be used in precise laser applications to avoid laser wavelength drifting as environment

temperature changes. Climate-controlled jackets are beginning to use Peltier elements. 

2. Science and imaging

Peltier elements are used in scientific devices. They are a common component in thermal cyclers,

used for the synthesis of DNA by polymerase chain reaction (PCR), a common molecular

biological technique which requires the rapid heating and cooling of the reaction mixture for

denaturation, primer annealing and enzymatic synthesis cycles.

The effect is used in satellites and spacecraft to counter the effect of direct sunlight on one side

of a craft by dissipating the heat over the cold shaded side, whereupon the heat is dissipated

by thermal radiation into space. Since 1961, some unmanned spacecraft (including

the Curiosity Mars rover) utilize radioisotope thermoelectric generators (RTGs) that convert

thermal energy into electrical energy using the Seebeck effect, lasting several decades, fueled by

the decay of high energy radioactive materials.

Photon detectors such as CCDs in astronomical telescopes or very high-end digital cameras are

often cooled down with Peltier elements. This reduces dark counts due to thermal noise. A dark

count occurs when a pixel registers an electron because of a thermal fluctuation rather than

because it has received a photon. On digital photos taken at low light these occur as speckles (or

"pixel noise").

Thermoelectric coolers can be used to cool computer components to keep temperatures within

design limits, or to maintain stable functioning when over clocking. A Peltier cooler with a heat

sink or water block can cool a chip to well below ambient temperature.

In fiber optic applications, where the wavelength of a laser or a component is highly dependent

on temperature, Peltier coolers are used along with a Thermistor in a feedback loop to maintain a

constant temperature and thereby stabilize the wavelength of the device.

Some electronic equipment intended for military use in the field is thermoelectrically cooled.

CHAPTER 3HEAT SINK

1.1 INTRODUCTION

In electronic systems, a heat sink is a passive heat exchanger component that cools a device by

dissipating heat into the surrounding air. In computers, heat sinks are used to cool central

processing units or graphics processors. Heat sinks are used with high-power semiconductor

devices such as power transistors and optoelectronic devices such as lasers and light emitting

diodes (LEDs), wherever the heat dissipation ability of the basic device package is insufficient to

control its temperature.

A heat sink is designed to increase the surface area in contact with the cooling medium

surrounding it, such as the air. Approach air velocity, choice of material, fin (or other protrusion)

design and surface treatment are some of the factors which affect the thermal performance of a

heat sink. Heat sink attachment methods and thermal interface materials also affect the

eventual die temperature of the integrated circuit. Thermal adhesive or thermal grease fills the air

gap between the heat sink and device to improve its thermal performance. Theoretical,

experimental and numerical methods can be used to determine a heat sink's thermal performance.

A fan-cooled heat sink on the processor of a personal computer. To the right is a smaller heat

sink cooling another integrated circuit of the motherboard.

2.2 HEAT TRANSFER PRINCIPLE

A heat sink transfers thermal energy from a higher temperature to a lower

temperature fluid medium. The fluid medium is frequently air, but can also be water or in the

case of heat exchangers, refrigerants and oil. If the fluid medium is water, the 'heat sink' is

frequently called a cold plate. In thermodynamics a heat sink is a heat reservoir that can absorb

an arbitrary amount of heat without significantly changing temperature. Practical heat sinks for

electronic devices must have a temperature higher than the surroundings to transfer heat by

convection, radiation, and conduction.

To understand the principle of a heat sink, consider Fourier's law of heat conduction. Joseph

Fourier was a French mathematician who made important contributions to the analytical

treatment of heat conduction. Fourier's law of heat conduction, simplified to a one-dimensional

form in the x-direction, shows that when there is a temperature gradient in a body, heat will be

transferred from the higher temperature region to the lower temperature region. The rate at which

heat is transferred by conduction,  , is proportional to the product of the temperature gradient

and the cross-sectional area through which heat is transferred.

Figure 2: Sketch of a heat sink in a duct used to calculate the governing equations from

conservation of energy and Newton’s law of cooling.

Consider a heat sink in a duct, where air flows through the duct, as shown in Figure 2. It is

assumed that the heat sink base is higher in temperature than the air. Applying the

conservation of energy, for steady-state conditions, and Newton’s law of cooling to the

temperature nodes shown in Figure 2 gives the following set of equations.

 (1)

 (2)

where

 (3)

Using the mean air temperature is an assumption that is valid for relatively short heat sinks.

When compact heat exchangers are calculated, the logarithmic mean air temperature is used.   

is the air mass flow rate in kg/s.

The above equations show that

When the air flow through the heat sink decreases, this results in an increase in the

average air temperature. This in turn increases the heat sink base temperature. And

additionally, the thermal resistance of the heat sink will also increase. The net result is a

higher heat sink base temperature.

The increase in heat sink thermal resistance with decrease in flow rate will be shown in

later in this article.

The inlet air temperature relates strongly with the heat sink base temperature. For

example, if there is recirculation of air in a product, the inlet air temperature is not the

ambient air temperature. The inlet air temperature of the heat sink is therefore higher,

which also results in a higher heat sink base temperature.

If there is no air flow around the heat sink, energy cannot be transferred.

A heat sink is not a device with the "magical ability to absorb heat like a sponge and send

it off to a parallel universe".

Natural convection requires free flow of air over the heat sink. If fins are not aligned vertically,

or if pins are too close together to allow sufficient air flow between them, the efficiency of the

heat sink will decline.

3.3 DESIGN PARAMETERS OF HEAT SINK

1. Thermal resistance

For semiconductor devices used in a variety of consumer and industrial electronics, the idea

of thermal resistance simplifies the selection of heat sinks. The heat flow between the

semiconductor die and ambient air is modeled as a series of resistances to heat flow; there is a

resistance from the die to the device case, from the case to the heat sink, and from the heat sink

to the ambient. The sum of these resistances is the total thermal resistance from the die to the

ambient. Thermal resistance is defined as temperature rise per unit of power, analogous to

electrical resistance, and is expressed in units of degrees Celsius per watt (°C/W). If the device

dissipation in watts is known, and the total thermal resistance is calculated, the temperature rise

of the die over ambient can be calculated.

The idea of thermal resistance of a semiconductor heat sink is an approximation. It does not take

into account non-uniform distribution of heat over a device or heat sink. It only models a system

in thermal equilibrium, and does not take into account the change in temperatures with time. Nor

does it reflect the non-linearity of radiation and convection with respect to temperature rise.

However, manufacturers tabulate typical values of thermal resistance for heat sinks and

semiconductor devices, which allows selection of commercially manufactured heat sinks to be

simplified.

Commercial extruded aluminum heat sinks have a thermal resistance (heat sink to ambient air)

ranging from 0.4 °C/W for a large sink meant for TO3 devices, up to as high as85 °C/W for a

clip-on heat sink for a TO92 small plastic case. The famous, popular, historic and

notable 2N3055 power transistor in a TO3 case has an internal thermal resistance from junction

to case of 1.52 °C/W. The contact between the device case and heat sink may have a thermal

resistance of between 0.5 up to 1.7 °C/W, depending on the case size, and use of grease or

insulating mica washer.

2. Material

The most common heat sink materials are aluminium alloys. Aluminium alloy 1050A has one of

the higher thermal conductivity values at 229 W/m•K  but is mechanically soft. Aluminium

alloys 6061 and 6063 are commonly used, with thermal conductivity values of 166 and 201

W/m•K, respectively. The values depend on the temper of the alloy.

Copper has excellent heat sink properties in terms of its thermal conductivity, corrosion

resistance, biofouling resistance, and antimicrobial resistance (see Main Article: Copper in heat

exchangers). Copper has around twice the thermal conductivity of aluminium and faster, more

efficient heat absorption. Its main applications are in industrial facilities, power plants, solar

thermal water systems, HVAC systems, gas water heaters, forced air heating and cooling

systems, geothermal heating and cooling, and electronic systems.

Copper is three times as dense and more expensive than aluminium. Copper heat sinks are

machined and skived. Another method of manufacture is to solder the fins into the heat sink

base. Aluminium can be extruded, but copper can not.

Diamond is another heat sink material, and its thermal conductivity of 2000 W/m•K exceeds

copper five-fold. In contrast to metals, where heat is conducted by delocalized electrons, lattice

vibrations are responsible for diamond's very high thermal conductivity. For thermal

management applications, the outstanding thermal conductivity and diffusivity of diamond is an

essential. Nowadays synthetic diamond is used as submounts for high-power integrated circuits

and laser diodes.

Composite materials can be used. Examples are a copper-tungsten pseudoalloy, AlSiC (silicon

carbide in aluminium matrix), Dymalloy (diamond in copper-silver alloy matrix), andE-

Material (beryllium oxide in beryllium matrix). Such materials are often used as substrates for

chips, as their thermal expansion coefficient can be matched to ceramics and semiconductors.

3. Fin efficiency

Fin efficiency is one of the parameters which makes a higher thermal conductivity material

important. A fin of a heat sink may be considered to be a flat plate with heat flowing in one end

and being dissipated into the surrounding fluid as it travels to the other.[9] As heat flows through

the fin, the combination of the thermal resistance of the heat sink impeding the flow and the heat

lost due to convection, the temperature of the fin and, therefore, the heat transfer to the fluid, will

decrease from the base to the end of the fin. Fin efficiency is defined as the actual heat

transferred by the fin, divided by the heat transfer were the fin to be isothermal (hypothetically

the fin having infinite thermal conductivity). Equations 6 and 7 are applicable for straight fins.

 (6)

 (7)

Where:

hf is the convection coefficient of the fin

Air: 10 to 100 W/(m2K)

Water: 500 to 10,000 W/(m2K)

k is the thermal conductivity of the fin material

Aluminium: 120 to 240 W/(m·K)

Lf is the fin height (m)

tf is the fin thickness (m)

Fin efficiency is increased by decreasing the fin aspect ratio (making them thicker or

shorter), or by using more conductive material (copper instead of aluminium, for

example).

4. SPREADING RESISTANCE

Another parameter that concerns the thermal conductivity of the heat sink material is spreading

resistance. Spreading resistance occurs when thermal energy is transferred from a small area to a

larger area in a substance with finite thermal conductivity. In a heat sink, this means that heat

does not distribute uniformly through the heat sink base. The spreading resistance phenomenon

is shown by how the heat travels from the heat source location and causes a large temperature

gradient between the heat source and the edges of the heat sink. This means that some fins are at

a lower temperature than if the heat source were uniform across the base of the heat sink. This no

uniformity increases the heat sink's effective thermal resistance.

To decrease the spreading resistance in the base of a heat sink:

Increase the base thickness

Choose a different material with better thermal conductivity

Use a vapor chamber or heat pipe in the heat sink base.

5. FIN ARRANGEMENTS

A pin fin heat sink is a heat sink that has pins that extend from its base. The pins can be

cylindrical, elliptical or square. A pin is by far one of the more common heat sink types available

on the market. A second type of heat sink fin arrangement is the straight fin. These run the entire

length of the heat sink. A variation on the straight fin heat sink is a cross cut heat sink. A straight

fin heat sink is cut at regular intervals.

In general, the more surface area a heat sink has, the better it works. However, this is not always

true. The concept of a pin fin heat sink is to try to pack as much surface area into a given volume

as possible. As well, it works well in any orientation. Kordyban has compared the performance of

a pin fin and a straight fin heat sink of similar dimensions. Although the pin fin has

194 cm2 surface area while the straight fin has 58 cm2, the temperature difference between the

heat sink base and the ambient air for the pin fin is 50 °C. For the straight fin it was 44 °C or 6

°C better than the pin fin. Pin fin heat sink performance is significantly better than straight fins

when used in their intended application where the fluid flows axially along the pins rather than

only tangentially across the pins.

A pin-, straight- and flared fin heat sink types

Comparison of a pin fin and straight fin heat sink of similar dimensions. Adapted from

data of

Heat sink fin typeWidth

[cm]

Length

[cm]

Height

[cm]

Surface

area

[cm²]

Volume

[cm³]

Temperature

difference,

Tcase−Tair [°C]

Straight 2.5 2.5 3.2 58 20 44

Pin 3.8 3.8 1.7 194 24 51

Another configuration is the flared fin heat sink; its fins are not parallel to each other, as shown

in figure 5. Flaring the fins decreases flow resistance and makes more air go through the heat

sink fin channel; otherwise, more air would bypass the fins. Slanting them keeps the overall

dimensions the same, but offers longer fins. Forghan, et al.  have published data on tests

conducted on pin fin, straight fin and flared fin heat sinks. They found that for low approach air

velocity, typically around 1 m/s, the thermal performance is at least 20% better than straight fin

heat sinks. Lasance and Eggink also found that for the bypass configurations that they tested, the

flared heat sink performed better than the other heat sinks tested.

6. SURFACE COLOR

The heat transfer from the heatsink occurs by convection of the surrounding air, conduction

through the air, and radiation.

Heat transfer by radiation is a function of both the heat sink temperature, and the temperature of

the surroundings that the heat sink is optically coupled with. When both of these temperatures

are on the order of 0 °C to 100 °C, the contribution of radiation compared to convection is

generally small, and this factor is often neglected. In this case, finned heat sinks operating in

either natural-convection or forced-flow will not be affected significantly by surface emissivity.

In situations where convection is low, such as a flat non-finned panel with low airflow, radiative

cooling can be a significant factor. Here the surface properties may be an important design

factor. Matte-black surfaces will radiate much more efficiently than shiny bare metal in the

visible spectrum. A shiny metal surface has low effective emissivity due to its low surface area.

While the emissivity of a material is tremendously energy (frequency) dependent, the noble

metals demonstrate very low emissivity in the Near-Infrared spectrum. The emissivity in the

visible spectrum is closely related to color. For most materials, the emissivity in the visible

spectrum is similar to the emissivity in the infrared spectrum; however there are exceptions,

notably certain metal oxides that are used as "selective surfaces".

In a vacuum or in outer space, there is no convective heat transfer, thus in these environments,

radiation is the only factor governing heat flow between the heat sink and the environment. For a

satellite in space, a 100 °C (373 Kelvin) surface facing the sun will absorb a lot of radiant heat,

since the sun's surface temperature is nearly 6000 Kelvin, whereas the same surface facing deep-

space will radiate a lot of heat, since deep-space has an effective temperature of only a few

Kelvin.

3.4 ENGINEERING APPLICATIONS OF HEAT SINK

Microprocessor cooling

Heat dissipation is an unavoidable by-product of electronic devices and circuits. In general, the

temperature of the device or component will depend on the thermal resistance from the

component to the environment, and the heat dissipated by the component. To ensure that the

component temperature does not overheat, a thermal engineer seeks to find an efficient heat

transfer path from the device to the environment. The heat transfer path may be from the

component to a printed circuit board (PCB), to a heat sink, to air flow provided by a fan, but in

all instances, eventually to the environment.

Two additional design factors also influence the thermal/mechanical performance of the thermal

design:

1. The method by which the heat sink is mounted on a component or processor. This will be

discussed under the section attachment methods.

2. For each interface between two objects in contact with each other, there will be a

temperature drop across the interface. For such composite systems, the temperature drop

across the interface may be appreciable. This temperature change may be attributed to

what is known as the thermal contact resistance. Thermal interface materials(TIM)

decrease the thermal contact resistance.

Attachment methods

As power dissipation of components increases and component package size decreases, thermal

engineers must innovate to ensure components won't overheat. Devices that run cooler last

longer. A heat sink design must fulfill both its thermal as well as its mechanical requirements.

Concerning the latter, the component must remain in thermal contact with its heat sink with

reasonable shock and vibration. The heat sink could be the copper foil of a circuit board, or else a

separate heat sink mounted onto the component or circuit board. Attachment methods include

thermally conductive tape or epoxy, wire-form z clips, flat spring clips, standoff spacers, and

push pins with ends that expand after installing.

Thermally conductive tape

Figure 6: Roll of thermally conductive tape.

Thermally conductive tape is one of the most cost-effective heat sink attachment materials. [14] It

is suitable for low-mass heat sinks and for components with low power dissipation. It consists of

a thermally conductive carrier material with a pressure-sensitive adhesive on each side.

This tape is applied to the base of the heat sink, which is then attached to the component.

Following are factors that influence the performance of thermal tape:[14]

1. Surfaces of both the component and heat sink must be clean, with no residue such as a

film of silicone grease.

2. Preload pressure is essential to ensure good contact. Insufficient pressure results in areas

of non-contact with trapped air, and results in higher-than-expected interface thermal

resistance.

3. Thicker tapes tend to provide better "wettability" with uneven component surfaces.

"Wettability" is the percentage area of contact of a tape on a component. Thicker tapes,

however, have a higher thermal resistance than thinner tapes. From a design standpoint,

it is best to strike a balance by selecting a tape thickness that provides maximum

"wettablilty" with minimum thermal resistance.

Epoxy

Epoxy is more expensive than tape, but provides a greater mechanical bond between the heat

sink and component, as well as improved thermal conductivity. The epoxy chosen must be

formulated for this purpose. Most epoxies are two-part liquid formulations that must be

thoroughly mixed before being applied to the heat sink, and before the heat sink is placed on the

component. The epoxy is then cured for a specified time, which can vary from 2 hours to 48

hours. Faster cure time can be achieved at higher temperatures. The surfaces to which the epoxy

is applied must be clean and free of any residue.

The epoxy bond between the heat sink and component is semi-permanent/permanent. This makes

re-work very difficult and at times impossible. The most typical damage caused by rework is the

separation of the component die heat spreader from its package.

Figure 7: A pin fin heat sink with a z-clip retainer.

Wire form Z-clips

More expensive than tape and epoxy, wire form z-clips attach heat sinks mechanically. To use

the z-clips, the printed circuit board must have anchors. Anchors can be either soldered onto the

board, or pushed through. Either type requires holes to be designed into the board. The use of

RoHS solder must be allowed for because such solder is mechanically weaker than traditional

Pb/Sn solder.

To assemble with a z-clip, attach one side of it to one of the anchors. Deflect the spring until the

other side of the clip can be placed in the other anchor. The deflection develops a spring load on

the component, which maintains very good contact. In addition to the mechanical attachment that

the z-clip provides, it also permits using higher-performance thermal interface materials, such as

phase change types.

Figure 8: Two heat sink attachment methods, namely the maxiGRIP (left) and Talon Clip

Clips

Available for processors and ball grid array (BGA) components, clips allow the attachment of a

BGA heat sink directly to the component. The clips make use of the gap created by the ball grid

array (BGA) between the component underside and PCB top surface. The clips therefore require

no holes in the PCB. They also allow for easy rework of components. Examples of commercially

available clips are the maxiGRIPand superGRIP range from Advanced Thermal Solutions (ATS)

and the Talon Clip from Malico. The three aforementioned clipping methods use plastic frames

for the clips, but the ATS designs uses metal spring clips to provide the compression force. The

Malico design uses the plastic "arm" to provide a mechanical load on the component. Depending

on the product requirement, the clipping methods will have to meet shock and vibration

standards, such as Telecordia GR-63-CORE, ETSI 300 019 and MIL-STD-810.

Figure 9: Push pins.

Push pins with compression springs

For larger heat sinks and higher preloads, push pins with compression springs are very

effective. The push pins, typically made of brass or plastic, have a flexible barb at the end that

engages with a hole in the PCB; once installed, the barb retains the pin. The compression spring

holds the assembly together and maintains contact between the heat sink and component. Care is

needed in selection of push pin size. Too great an insertion force can result in the die cracking

and consequent component failure.

Threaded standoffs with compression springs

For very large heat sinks, there is no substitute for the threaded standoff and compression spring

attachment method. A threaded standoff is essentially a hollow metal tube with internal threads.

One end is secured with a screw through a hole in the PCB. The other end accepts a screw which

compresses the spring, completing the assembly. A typical heat sink assembly uses two to four

standoffs, which tends to make this the most costly heat sink attachment design. Another

disadvantage is the need for holes in the PCB.

Thermal interface materials

Thermal contact resistance occurs due to the voids created by surface roughness effects, defects

and misalignment of the interface. The voids present in the interface are filled with air. Heat

transfer is therefore due to conduction across the actual contact area and to conduction (or

natural convection) and radiation across the gaps. If the contact area is small, as it is for rough

surfaces, the major contribution to the resistance is made by the gaps. To decrease the thermal

contact resistance, the surface roughness can be decreased while the interface pressure is

increased. However, these improving methods are not always practical or possible for electronic

equipment. Thermal interface materials (TIM) are a common way to overcome these limitations,

Properly applied thermal interface materials displace the air that is present in the gaps between

the two objects with a material that has a much-higher thermal conductivity. Air has a thermal

conductivity of 0.022 W/m•K while TIMs have conductivities of 0.3 W/m•K and higher.

When selecting a TIM, care must be taken with the values supplied by the manufacturer. Most

manufacturers give a value for the thermal conductivity of a material. However, the thermal

conductivity does not take into account the interface resistances. Therefore, if a TIM has a high

thermal conductivity, it does not necessarily mean that the interface resistance will be low.

Selection of a TIM is based on three parameters: the interface gap which the TIM must fill, the

contact pressure, and the electrical resistivity of the TIM. The contact pressure is the pressure

applied to the interface between the two materials. The selection does not include the cost of the

material. Electrical resistivity may, or may not, be important, depending upon electrical design

details.

3.5 PERFORMANCE OF HEAT SINK

In general, a heat sink performance is a function of material thermal conductivity, dimensions,

fin type, heat transfer coefficient, air flow rate, and duct size. To determine the thermal

performance of a heat sink, a theoretical model can be made. Alternatively, the thermal

performance can be measured experimentally. Due to the complex nature of the highly 3D flow

in present in applications, numerical methods or computational fluid dynamics (CFD) can also be

used. This section will discuss the aforementioned methods for the determination of the heat sink

thermal performance.

A heat transfer theoretical model

Figure 13: Sketch of a heat sink with equivalent thermal resistances.

One of the methods to determine the performance of a heat sink is to use heat transfer and fluid

dynamics theory. One such method has been published by Jeggels, et al., [20]though this work is

limited to ducted flow. Ducted flow is where the air is forced to flow through a channel which

fits tightly over the heat sink. This makes sure that all the air goes through the channels formed

by the fins of the heat sink. When the air flow is not ducted, a certain percentage of air flow will

bypass the heat sink. Flow bypass was found to increase with increasing fin density and

clearance, while remaining relatively insensitive to inlet duct velocity.[21]

The heat sink thermal resistance model consists of two resistances, namely the resistance in the

heat sink base,  , and the resistance in the fins,  . The heat sink base thermal resistance,  ,

can be written as follows if the source is a uniformly applied the heat sink base. If it is not, then

the base resistance is primarily spreading resistance:

 (4)

where   is the heat sink base thickness,   is the heat sink material thermal conductivity

and   is the area of the heat sink base.

The thermal resistance from the base of the fins to the air,  , can be calculated by the

following formulas.

 (5)

[10] (6)

[10] (7)

 (8)

 (9)

[22] (10)

[22] (11)

 (12)

 (13)

The flow rate can be determined by the intersection of the heat sink system curve and the fan

curve. The heat sink system curve can be calculated by the flow resistance of the channels and

inlet and outlet losses as done in standard fluid mechanics text books, such as Potter, et al.[23] and

White.

Once the heat sink base and fin resistances are known, then the heat sink thermal resistance,   

can be calculated as:   (14)

Using the equations 5 to 13 and the dimensional data in, the thermal resistance for the fins was

calculated for various air flow rates. The data for the thermal resistance and heat transfer

coefficient are shown in Figure 14. It shows that shows that for an increasing air flow rate, the

thermal resistance of the heat sink decreases.

Experimental methods

Experimental tests are one of the more popular ways to determine the heat sink thermal

performance. In order to determine the heat sink thermal resistance, the flow rate, input power,

inlet air temperature and heat sink base temperature need to be known. Figure 2 shows a test

setup for a ducted flow heat sink application. Vendor-supplied data is commonly provided for

ducted test results.[25] However, the results are optimistic and can give misleading data when heat

sinks are used in an unducted application. More details on heat sink testing methods and

common oversights can be found in Azar, et al

Numerical methods

Figure 16: Radial heat sink with thermal profile and swirling forced convection flow trajectories

predicted using a CFD analysis package

In industry, thermal analyses are often ignored in the design process or performed too

late — when design changes are limited and become too costly. Of the three methods mentioned

in this article, theoretical and numerical methods can be used to determine an estimate of the heat

sink or component temperatures of products before a physical model has been made. A

theoretical model is normally used as a first order estimate. Numerical methods or computational

fluid dynamics (CFD) provide a qualitative (and sometimes even quantitative) prediction of fluid

flows. What this means is that it will give a visual or post-processed result of a simulation, like

the images in figures 16 and 17, and the CFD animations in figure 18 and 19, but the quantitative

or absolute accuracy of the result is sensitive to the inclusion and accuracy of the appropriate

parameters.

CFD can give an insight into flow patterns that are difficult, expensive or impossible to study

using experimental methods. Experiments can give a quantitative description of flow phenomena

using measurements for one quantity at a time, at a limited number of points and time instances.

If a full scale model is not available or not practical, scale models or dummy models can be used.

The experiments can have a limited range of problems and operating conditions. Simulations can

give a prediction of flow phenomena using CFD software for all desired quantities, with high

resolution in space and time and virtually any problem and realistic operating conditions.

However, if critical, the results may need to be validated.

CHAPTER – 4

4.1 RESULT, MODIFICATIONS AND FUTURE SCOPE

Thermoelectric Genrator Designed has been working efficiently and The idea behind this project

was to utilize a small temperature difference between the ice / cold water and some atmospheric

heat to produce electricity using thermoelectric generator.

4.2 EFFICIENCY OF THERMOELECTRIC GENERATOR

Currently, ATEGs are about 5% efficient. However, advancements in thin-film and quantum

well technologies could increase efficiency up to 15% in the future.

The efficiency of an ATEG is governed by the thermoelectric conversion efficiency of the

materials and the thermal efficiency of the two heat exchangers. The ATEG efficiency can be

expressed as: mridulkapri@ymail.com

ζOV = ζCONV х ζHX х ρ

Where:

ζOV : The overall efficiency of the ATEG

ζCONV : Conversion efficiency of thermoelectric materials

ζHX: Efficiency of the heat exchangers

ρ : The ratio between the heat passed through thermoelectric materials to that passed from the hot

side to the cold side

REFERENCES

[1] Heat Loss from Electrical and Control Equipment in Industrial Plants: Part-Methods and Scope, Warren N. White, Ph.D, 2004[2] Solar refrigeration using the Peltier Effect J C. Swart Cape Technikon, 1996[3] Efficiency Performance of a Refrigerated Plate based on the Peltier Effect Potentially Supplied by Solar Energy, M. S. Carvalho[4] Solar Powered Refrigeration for Transport Applications, David Bergeron[5] Thermo electric effect, Wikipedia [6] Reiyu Chein, Guanming Huang – “Thermoelectric cooler application in electronic cooling”, Applied Thermal Engineering (2004), ELSEVIER; [7] H. Sofrata – “Heat rejection alternatives for thermoelectric refrigerators”, Energy Conversion & Management 37 (1996) 269-280, PERGAMON;[8] P. Corrèges, E. Bugnard, C. Millerin, A. Masiero,, J.P. Andrivet, A. Bloc, Y. Dunant – “A simple, low-cost and fast Peltier thermoregulation set-up for electrophysiology”, Journal of Neuroscience Methods 83 (1998) 177-184, ELSEVIER; [9] Incropera, P. Frank, De Witt, P. David – “Fundamentals of Heat and Mass Transfer”, 5 th Edition, Wiley & Sons;[10] Ioffe, Af – “Semiconductor and thermoelectric cooling”, London: Infosearch, 1957;[11] John Merchant, Mikron Instrument Company, Inc – “Infrared Temperature, Measurement Theory and Application” – Omega Handbook;[12] Jun Luo, Lingen Chen, Fengrui Sun, Chih Wu – “ Optimum allocation of heat transfer surface area for cooling load and COPoptimization of a thermoelectric refrigerator”, Energy Convertion and Management 44 (2003) 3197-3206, PERGAMON;[13] Ken Sato, Haruhiko Okumura, Satarou Yamaguchi – “Numerical Calculations for Peltier current lead designing”, Cryogenics 41 (2001) 497-503, ELSEVIER;[14] Lawton, B. and Klingenberg, G. – “Transient Temperature In Engineering and Science”, Oxford Science Publications, 1996;[15] Maria João Rodrigues – “Building-Integrated Photovoltaics: A Policy Recommendation for Portugal” – Post-Graduation Dissertation Thesis, Instituto Superior Técnico, 2000;[16] Maria João Rodrigues - “Porque Falha a Energia Solar em Portugal?” – Público -Daily Newspaper, 29 de Dezembro de 2003;[17] Melcor Thermal Solutions Catalog;[18] “On being a scientist-Responsible conduct in research” – Committee on Science, Engineering, and Public Policy – National Academy Press, Washington D.C., 1995;[19] Paulo Manuel Cadete Ferrão – “Análise Experimental de Chamas Turbulentas com Recirculação” – Post-Graduation Dessertation Thesis, Instituto Superior Técnico, 1993;